Android has supported 3rd party keyboards for years, but the feature is new to iOS. Third party keyboards are commonly used to offer different ways of entering text, by swiping, for example.

Custom keyboards can be used for more than just typing. They can also be developed with a new “scan” button that, when tapped, uses the camera to scan a barcode and enter the text or numbers from that barcode anywhere you can type: web pages, email, other apps, etc.